A cylinder head gasket and an exhaust manifold gasket of an engine of an automobile, a motorcycle or the like are exposed to repetitive pressure variations under high temperature, high pressure and high vibrations inherent to the engine. In particular, since a high pressure is applied to the cylinder gasket of the automobile engine upon compression, it is necessary for both contact party materials to contact with a high contact pressure (surface pressure) so as to keep the sealability. A metal gasket to be used for the engine or an exhaust gas passage is generally formed with a bead of a predetermined height (a continuous raised portion) so as to secure the sufficient contact pressure. The bead is normally formed by bead press forming. Therefore, a material steel sheet for manufacturing this kind of metal gasket is required to have high strength, high fatigue characteristic and excellent workability.
In the related art, work-hardened metastable austenitic stainless steel (SUS301 or the like) is heavily used for the gasket to be applied to the automobile engine or the exhaust gas passage. This kind of steel is intended to increase the strength by forming deformation-induced martensite with cold rolling. In order to increase the strength level, it is necessary to increase a cold rolling ratio. The increase in cold rolling ratio lowers the toughness, fatigue resistance and workability. Also, textures are remarkably developed and a characteristic difference between a rolling-parallel direction (L direction) and a rolling-perpendicular direction (C direction), i.e., anisotropy increases.
Also, a painted metal gasket may be used for an industrial piping or the like. This kind of metal gasket is required to have coating adhesion, in addition to the workability and the fatigue characteristic.
In the meantime, martensitic stainless steel is a material intended to increase the strength without depending on the increase in the cold rolling ratio. PTL 1 discloses applying martensitic steel grade to a gasket.